In a conventional optical transmission system, a super channel technique that subjects a plurality of subcarriers to high-density frequency multiplexing has been attracting attention for increasing the capacity of a trunk optical communication network. In the optical transmission system, narrow band reception by coherent detection and spectral shaping and waveform restoration by a digital signal processing contribute to the realization of the high-density frequency multiplexing. Meantime, an oscillation frequency deviation in a wavelength variable light source that occurs on the order of GHz causes crosstalk between the subcarriers and results in characteristic deterioration. The super channel technique that arranges frequency intervals in high density is significantly influenced by this problem.
In this regard, Patent Literature 1 below discloses a technique for transmitting a reduced optical power of a specific wavelength from a transmission side, and evaluating, at a reception side, a channel crosstalk amount from a bit error rate of a channel adjacent to the specific wavelength. A deviation in the wavelength of the channel having the optical power reduced is detected on the basis of the channel crosstalk amount, and the wavelength deviation of the channel having the optical power reduced at the transmission side is compensated.